Electrically Conductive Pins For Microcircuit Tester

ABSTRACT

The terminals of a device under test (DUT) are temporarily electrically connected to corresponding contact pads on a load board by a series of electrically conductive pin pairs. The pin pairs are held in place by an interposer membrane with a top facing the device under test, a bottom facing the load board, and a vertically resilient, non-conductive member between the top and bottom contact plates. Each pin pair includes a top and bottom pin, which extend beyond the top and bottom contact plates, respectively, toward the device under test and the load board, respectively. The bottom pins has a lower contact surface which includes an arcuate portion or ridge which increases contact pressure and ablates oxides by the rocking action of ridge when the DUT in inserted.

CROSS REFERENCE AND INCORPORATION BY REFERENCE

This application is a Continuation in Part (CIP) of Ser. No. 13/226,606filed 7 Sep. 2011 which is based on a provisional application Ser. No.61/380,494 filed 7 Sep. 2010 and provisional application Ser. No.61/383,411 filed 16 Sep. 2010 and this application also is aContinuation of Ser. No. 12/721,039 filed 10 Mar. 2010 and published asUS-2010/0231251-A1. Each of the above applications is to be consideredincorporated by reference.

BACKGROUND OF THE DISCLOSURE

1. Field of the Disclosure

The present disclosure is directed to equipment for testingmicrocircuits.

2. Description of the Related Art

As microcircuits continually evolve to be smaller and more complex, thetest equipment that tests the microcircuits also evolves. There is anongoing effort to improve microcircuit test equipment, with improvementsleading to an increase in reliability, an increase in throughput, and/ora decrease in expense.

Mounting a defective microcircuit on a circuit board is relativelycostly. Installation usually involves soldering the microcircuit ontothe circuit board. Once mounted on a circuit board, removing amicrocircuit is problematic because the very act of melting the solderfor a second time ruins the circuit board. Thus, if the microcircuit isdefective, the circuit board itself is probably ruined as well, meaningthat the entire value added to the circuit board at that point is lost.For all these reasons, a microcircuit is usually tested beforeinstallation on a circuit board.

Each microcircuit must be tested in a way that identifies all defectivedevices, but yet does not improperly identify good devices as defective.Either kind of error, if frequent, adds substantial overall cost to thecircuit board manufacturing process, and can add retest costs fordevices improperly identified as defective devices.

Microcircuit test equipment itself is quite complex. First of all, thetest equipment must make accurate and low resistance temporary andnon-destructive electrical contact with each of the closely spacedmicrocircuit contacts. Because of the small size of microcircuitcontacts and the spacings between them, even small errors in making thecontact will result in incorrect connections. Connections to themicrocircuit that are misaligned or otherwise incorrect will cause thetest equipment to identify the device under test (DUT) as defective,even though the reason for the failure is the defective electricalconnection between the test equipment and the DUT rather than defects inthe DUT itself.

A further problem in microcircuit test equipment arises in automatedtesting. Testing equipment may test 100 devices a minute, or even more.The sheer number of tests cause wear on the tester contacts makingelectrical connections to the microcircuit terminals during testing.This wear dislodges conductive debris from both the tester contacts andthe DUT terminals that contaminates the testing equipment and the DUTsthemselves.

The debris eventually results in poor electrical connections duringtesting and false indications that the DUT is defective. The debrisadhering to the microcircuits may result in faulty assembly unless thedebris is removed from the microcircuits. Removing debris adds cost andintroduces another source of defects in the microcircuits themselves.

Other considerations exist as well. Inexpensive tester contacts thatperform well are advantageous. Minimizing the time required to replacethem is also desirable, since test equipment is expensive. If the testequipment is off line for extended periods of normal maintenance, thecost of testing an individual microcircuit increases.

Test equipment in current use has an array of test contacts that mimicthe pattern of the microcircuit terminal array. The array of testcontacts is supported in a structure that precisely maintains thealignment of the contacts relative to each other. An alignment templateor board aligns the microcircuit itself with the test contacts. The testcontacts and the alignment board are mounted on a load board havingconductive pads that make electrical connection to the test contacts.The load board pads are connected to circuit paths that carry thesignals and power between the test equipment electronics and the testcontacts.

For the electrical tests, it is desired to form a temporary electricalconnection between each terminal on the device under test and acorresponding electrical pad on a load board. In general, it isimpractical to solder and remove each electrical terminal on themicrocircuit being contacted by a corresponding electrical probe on thetestbed. Instead of soldering and removing each terminal, the tester mayemploy a series of electrically conductive pins arranged in a patternthat corresponds to both the terminals on the device under test and theelectrical pads on the load board. When the device under test is forcedinto contact with the tester, the pins complete the circuits betweenrespective device under test contacts and corresponding load board pads.After testing, when the device under test is released, the terminalsseparate from the pins and the circuits are broken.

The present application is directed to improvements to these pins.

There is a type of testing known as “Kelvin” testing, which measures theresistance between two terminals on the device under test. Basically,Kelvin testing involves forcing a current to flow between the twoterminals, measuring the voltage difference between the two terminals,and using Ohm's Law to derive the resistance between the terminals,given as the voltage divided by the current. Each terminal on the deviceunder test is electrically connected to two contact pads on the loadboard. One of the two pads supplies a known current amount of current.The other pad is a high-impedance connection that acts as a voltmeter,which does not draw any significant amount of current. In other words,each terminal on the device under test that is to undergo Kelvin testingis simultaneously electrically connected to two pads on the loadboard—one pad supplying a known amount of current and the other padmeasuring a voltage and drawing an insignificant amount of current whiledoing so. The terminals are Kelvin tested two at a time, so that asingle resistance measurement uses two terminals on the load board andfour contact pads.

In this application, the pins that form the temporary electricalconnections between the device under test and the load board may be usedin several manners. In a “standard” test, each pin connects a particularterminal on the device under test to a particular pad on the load board,with the terminals and pads being in a one-to-one relationship. Forthese standard tests, each terminal corresponds to exactly one pad, andeach pad corresponds to exactly one terminal. In a “Kelvin” test, thereare two pins contacting each terminal on the device under test, asdescribed above. For these Kelvin tests, each terminal (on the deviceunder test) corresponds to two pads (on the load board), and each pad(on the load board) corresponds to exactly one terminal (on the deviceunder test). Although the testing scheme may vary, the mechanicalstructure and use of the pins is essentially the same, regardless of thetesting scheme.

There are many aspects of the testbeds that may be incorporated fromolder or existing testbeds. For instance, much of the mechanicalinfrastructure and electrical circuitry may be used from existing testsystems, and may be compatible with the electrically conductive pinsdisclosed herein. Such existing systems are listed and summarized below.

An exemplary microcircuit tester is disclosed in United States PatentApplication Publication Number US 2007/0202714 A1, titled “Test contactsystem for testing integrated circuits with packages having an array ofsignal and power contacts”, invented by Jeffrey C. Sherry, published onAug. 30, 2007 and incorporated by reference herein in its entirety.

For the tester of '714, a series of microcircuits is testedsequentially, with each microcircuit, or “device under test”, beingattached to a testbed, tested electrically, and then removed from thetestbed. The mechanical and electrical aspects of such a testbed aregenerally automated, so that the throughput of the testbed may be keptas high as possible.

In '714, a test contact element for making temporary electrical contactwith a microcircuit terminal comprises at least one resilient fingerprojecting from an insulating contact membrane as a cantilevered beam.The finger has on a contact side thereof, a conducting contact pad forcontacting the microcircuit terminal. Preferably the test contactelement has a plurality of fingers, which may advantageously have apie-shaped arrangement. In such an arrangement, each finger is definedat least in part by two radially oriented slots in the membrane thatmechanically separate each finger from every other finger of theplurality of fingers forming the test contact element.

In '714, a plurality of the test contact elements can form a testcontact element array comprising the test contact elements arranged in apredetermined pattern. A plurality of connection vias are arranged insubstantially the predetermined pattern of the test contacts elements,with each of said connection vias is aligned with one of the testcontact elements. Preferably, an interface membrane supports theplurality of connection vias in the predetermined pattern. Numerous viascan be embedded into the pie pieces away from the device contact area toincrease life. Slots separating fingers could be plated to create anI-beam, thereby preventing fingers from deforming, and also increasinglife.

The connection vias of '714 may have a cup shape with an open end, withthe open end of the cup-shaped via contacting the aligned test contactelement. Debris resulting from loading and unloading DUTs from the testequipment can fall through the test contact elements where thecup-shaped vias impound the debris.

The contact and interface membranes of '714 may be used as part of atest receptacle including a load board. The load board has a pluralityof connection pads in substantially the predetermined pattern of thetest contacts elements. The load board supports the interface membranewith each of the connection pads on the load board substantially alignedwith one of the connection vias and in electrical contact therewith.

In '714, the device uses a very thin conductive plate with retentionproperties that adheres to a very thin non-conductive insulator. Themetal portion of the device provides multiple contact points or pathsbetween the contacting I/O and the load board. This can be done eitherwith a plated via hole housing or with plated through hole vias, orbumped surfaces, possibly in combination with springs, that has thefirst surface making contact with the second surface, i.e., the deviceI/O. The device I/O may be physically close to the load board, thusimproving electrical performance.

One particular type of microcircuit often tested before installation hasa package or housing having what is commonly referred to as a ball gridarray (BGA) terminal arrangement. A typical BGA package may have theform of a flat rectangular block, with typical sizes ranging from 5 mmto 40 mm on a side and 1 mm thick.

A typical microcircuit has a housing enclosing the actual circuitry.Signal and power (S&P) terminals are on one of the two larger, flatsurfaces, of the housing. Typically, terminals occupy most of the areabetween the surface edges and any spacer or spacers. Note that in somecases, a spacer may be an encapsulated chip or a ground pad.

Each of the terminals may include a small, approximately sphericalsolder ball that firmly adheres to a lead from the internal circuitrypenetrating surface, hence the term “ball grid array.” Each terminal andspacer project a small distance away from the surface, with theterminals projecting farther from the surface than the spacers. Duringassembly, all terminals are simultaneously melted, and adhere tosuitably located conductors previously formed on the circuit board.

The terminals themselves may be quite close to each other. Some havecenterline spacings of as little as 0.4 mm, and even relatively widelyspaced terminals may still be around 1.5 mm apart. Spacing betweenadjacent terminals is often referred to as “pitch.”

In addition to the factors mentioned above, BGA microcircuit testinginvolves additional factors.

First, in making the temporary contact with the ball terminals, thetester should not damage the S&P terminal surfaces that contact thecircuit board, since such damage may affect the reliability of thesolder joint for that terminal.

Second, the testing process is more accurate if the length of theconductors carrying the signals is kept short. An ideal test contactarrangement has short signal paths.

Third, solders commonly in use today for BGA terminals are mainly tinfor environmental purposes. Tin-based solder alloys are likely todevelop an oxide film on the outer surface that conducts poorly. Oldersolder alloys include substantial amounts of lead, which do not formoxide films. The test contacts must be able to penetrate the oxide filmpresent.

BGA test contacts currently known and used in the art employ spring pinsmade up of multiple pieces including a spring, a body and top and bottomplungers.

United States Patent Application Publication No. US 2003/0192181 A1,titled “Method of making an electronic contact” and published on Oct.16, 2003, shows microelectronic contacts, such as flexible, tab-like,cantilever contacts, which are provided with asperities disposed in aregular pattern. Each asperity has a sharp feature at its tip remotefrom the surface of the contact. As mating microelectronic elements areengaged with the contacts, a wiping action causes the sharp features ofthe asperities to scrape the mating element, so as to provide effectiveelectrical interconnection and, optionally, effective metallurgicalbonding between the contact and the mating element upon activation of abonding material.

According to United States Patent Application Publication No. US2004/0201390 A1, titled “Test interconnect for bumped semiconductorcomponents and method of fabrication” and published on Oct. 14, 2004, aninterconnect for testing semiconductor components includes a substrate,and contacts on the substrate for making temporary electricalconnections with bumped contacts on the components. Each contactincludes a recess and a pattern of leads cantilevered over the recessconfigured to electrically engage a bumped contact. The leads areadapted to move in a z-direction within the recess to accommodatevariations in the height and planarity of the bumped contacts. Inaddition, the leads can include projections for penetrating the bumpedcontacts, a non-bonding outer layer for preventing bonding to the bumpedcontacts, and a curved shape which matches a topography of the bumpedcontacts. The leads can be formed by forming a patterned metal layer onthe substrate, by attaching a polymer substrate with the leads thereonto the substrate, or by etching the substrate to form conductive beams.

According to U.S. Pat. No. 6,246,249 B1, titled “Semiconductorinspection apparatus and inspection method using the apparatus” andissued on Jun. 12, 2001 to Fukasawa, et al., a semiconductor inspectionapparatus performs a test on a to-be-inspected device which has aspherical connection terminal. This apparatus includes a conductor layerformed on a supporting film. The conductor layer has a connectionportion. The spherical connection terminal is connected to theconnection portion. At least a shape of the connection portion ischangeable. The apparatus further includes a shock absorbing member,made of an elastically deformable and insulating material, for at leastsupporting the connection portion. A test contact element of thedisclosure for making temporary electrical contact with a microcircuitterminal comprises at least one resilient finger projecting from aninsulating contact membrane as a cantilevered beam. The finger has on acontact side thereof, a conducting contact pad for contacting themicrocircuit terminal.

In U.S. Pat. No. 5,812,378, titled “Microelectronic connector forengaging bump leads” and issued on Sep. 22, 1998 to Fjelstad, et al., aconnector for microelectronic includes a sheet-like body having aplurality of holes, desirably arranged in a regular grid pattern. Eachhole is provided with a resilient laminar contact such as a ring of asheet metal having a plurality of projections extending inwardly overthe hole of a first major surface of the body. Terminals on a secondsurface of the connector body are electrically connected to thecontacts. The connector can be attached to a substrate such amulti-layer circuit panel so that the terminals on the connector areelectrically connected to the leads within the substrate.Microelectronic elements having bump leads thereon may be engaged withthe connector and hence connected to the substrate, by advancing thebump leads into the holes of the connector to engage the bump leads withthe contacts. The assembly can be tested, and if found acceptable, thebump leads can be permanently bonded to the contacts. According toUnited States Patent Application Publication No. US 2001/0011907 A1,titled “Test interconnect for bumped semiconductor components and methodof fabrication” and published on Aug. 9, 2001, an interconnect fortesting semiconductor components includes a substrate, and contacts onthe substrate for making temporary electrical connections with bumpedcontacts on the components. Each contact includes a recess and a supportmember over the recess configured to electrically engage a bumpedcontact. The support member is suspended over the recess on spiral leadsformed on a surface of the substrate. The spiral leads allow the supportmember to move in a z-direction within the recess to accommodatevariations in the height and planarity of the bumped contacts. Inaddition, the spiral leads twist the support member relative to thebumped contact to facilitate penetration of oxide layers thereon. Thespiral leads can be formed by attaching a polymer substrate with theleads thereon to the substrate, or by forming a patterned metal layer onthe substrate. In an alternate embodiment contact, the support member issuspended over the surface of the substrate on raised spring segmentleads.

BRIEF SUMMARY OF THE DISCLOSURE

An embodiment is a replaceable, longitudinally compressible membrane(10) for forming a plurality of temporary mechanical and electricalconnections between a device under test (1) having a plurality ofterminals (2) and a load board (3) having a plurality of contact pads(4), each contact pad (4) being laterally arranged to correspond toexactly one terminal (2), comprising: a flexible, electricallyinsulating top contact plate (40) longitudinally adjacent to theterminals (2) on the device under test (1); a flexible, electricallyinsulating bottom contact plate (60) longitudinally adjacent to thecontact pads (4) on the load board (3); a longitudinally resilient,electrically insulating interposer (50) between the top and bottomcontact plates (40, 60); a plurality of longitudinally compressible,electrically conductive pin pairs (20, 30) extending throughlongitudinal holes in the top contact plate (40), the interposer (50)and the bottom contact plate (60), each pin pair in the plurality beinglaterally arranged to correspond to exactly one terminal (2) on thedevice under test (1). When a particular pin pair (20, 30) islongitudinally compressed, the pins (20, 30) in the pair slide past eachother along a virtual interface surface (70) that is inclined withrespect to a surface normal of the interposer (50).

Another embodiment is a test fixture (5), comprising: a membrane (10)extending laterally between a device under test (1) and a load board(3), the device under test (1) including a plurality of electricalterminals (2) arranged in a predetermined pattern, the load board (3)including a plurality of electrical contact pads (4) arranged in apredetermined pattern corresponding to that of the terminals (2), themembrane having a top side facing the terminals (2) of the device undertest (1) and a bottom side facing the contact pads (4) of the load board(3); a plurality of electrical pin pairs (20, 30) supported by themembrane (10) in a predetermined pattern corresponding to that of theterminals (2), each pin pair in the plurality comprising: a top pin (20)extending through the top side of the membrane (10) and having a top pinmating surface (23); and a bottom pin (30) extending through the bottomside of the membrane (10) and having a bottom pin mating surface (33).The top and bottom pin mating surfaces (23, 33) have complementarysurface profiles. When the corresponding electrical terminal (2) isforced against the pin pair, the top and bottom pin mating surfaces (23,33) slide along each other along a virtual interface surface (70). Thevirtual interface surface (70) is inclined with respect to a surfacenormal of the membrane (10).

A further embodiment is a test fixture (5) for forming a plurality oftemporary mechanical and electrical connections between a device undertest (1) having a plurality of terminals (2) and a load board (3) havinga plurality of contact pads (4), the terminals (2) and contact pads (4)being arranged in a one-to-one correspondence, comprising: a replaceableinterposer membrane (10) disposed generally parallel to and adjacent tothe load board (3), the interposer membrane (10) including a pluralityof pin pairs (20, 30) arranged in a one-to-one correspondence with theplurality of terminals (2), each pin pair (20, 30) including a top pin(20) adjacent to the corresponding terminal (2) and extending into theinterposer membrane, and a bottom pin (30) adjacent to the correspondingcontact pad (4) and extending into the interposer membrane (10). Eachcontact pad (4) corresponding to a particular pin pair (20, 30) isconfigured to mechanically and electrically receive the terminal (2) onthe device under test (1) corresponding to the particular pin pair (20,30). When the device under test (1) is attached to the test fixture (5),the top pins (20) contact the corresponding terminals (2) on the deviceunder test (1), the bottom pins (30) contact the corresponding contactpads (4) on the load board (3), each top pin (20) contacts thecorresponding bottom pin (30) along a virtual interface surface that isinclined with respect to a surface normal of the interposer membrane(10), and the plurality of terminals (2) on the device under test (1)are electrically connected in a one-to-one correspondence to theplurality of contact pads (4) on the load board (3).

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a side-view drawing of a portion of the test equipment forreceiving a device under test (DUT).

FIG. 2 is a side-view drawing of the test equipment of FIG. 1, with theDUT electrically engaged.

FIG. 3 is a side-view cross-sectional drawing of an exemplary interposermembrane in its relaxed state.

FIG. 4 is a side-view cross-sectional drawing of the interposer membraneof FIG. 3, in its compressed state.

FIG. 5 is a side-view drawing of an exemplary pin pair in its relaxedstate.

FIG. 6 is a side-view drawing of the pin pair of FIG. 5, in itscompressed state.

FIG. 7 is a plan drawing of the planar interface surface shown in FIG.3.

FIG. 8 is a plan drawing of the cylindrically curved interface surfaceshown in FIG. 5.

FIG. 9 is a plan drawing of a curved interface surface that hascurvature in both horizontal and vertical directions.

FIG. 10 is a plan drawing of a saddle-shaped interface surface, in whichthe vertical and horizontal curvatures have opposite concavity.

FIG. 11 is a plan drawing of an interface surface having a locatingfeature, such as a groove or ridge.

FIG. 12 is a plan drawing of a generally planar top contact pad.

FIG. 13 is a plan drawing of a top contact pad that extends out of theplane of the pad.

FIG. 14 is a plan drawing of a top contact pad that includes aprotrusion out of the plane of the pad.

FIG. 15 is a plan drawing of a top contact pad that includes multipleprotrusions out of the plane of the pad.

FIG. 16 is a plan drawing of an inclined top contact pad.

FIG. 17 is a plan drawing of an inclined top contact pad with multipleprotrusions out of the plane of the pad.

FIG. 18 is a plan drawing of a textured top contact pad.

FIG. 19 is a plan drawing of a radially enlarged top contact pad.

FIG. 20 is a side-view drawing of a top pin with a top contact pad thathas rounded edges.

FIG. 21 is a side-view cross-sectional drawing of a top pin having a toppin engagement feature on one side.

FIG. 22 is a side-view cross-sectional drawing of a top pin having a toppin engagement feature on two opposing sides.

FIG. 23 is a side-view cross-sectional drawing of a top pin having a twotop pin engagement features engaging the top contact plate, and oneengagement feature engaging the foam interposer.

FIG. 24 is a side-view cross-sectional drawing of a bottom pin having abottom pin engagement feature.

FIG. 25 is a perspective-view cross-sectional drawing of an exemplaryinterposer membrane.

FIG. 26 is an end-on cross-sectional drawing of the interposer membraneof FIG. 25.

FIG. 27 is a plan drawing of the interposer membrane of FIGS. 25 and 26.

FIG. 28 is a plan drawing of an exemplary top contact pad for Kelvintesting, with an insulating portion that separates the two halves of thepad.

FIG. 29 is a side-view drawing of an exemplary pin pair for Kelvintesting, with an insulating ridge that extends outward from the top pinmating surface.

FIG. 30 is a plan drawing of an interposer membrane, inserted into aframe.

FIG. 31 is a plan drawing of the interposer membrane of FIG. 30, removedfrom the frame.

FIG. 32 a is a top-view schematic drawing of the interposer membrane ofFIGS. 30-31.

FIG. 32 b is a plan drawing of the interposer membrane of FIGS. 30-31.

FIG. 32 c is a front-view schematic drawing of the interposer membraneof FIGS. 30-31.

FIG. 32 d is a right-side-view schematic drawing of the interposermembrane of FIGS. 30-31.

FIG. 33 a is a top-view schematic drawing of the interposer, from theinterposer membrane of FIGS. 30-32.

FIG. 33 b is a plan drawing of the interposer, from the interposermembrane of FIGS. 30-32.

FIG. 33 c is a front-view schematic drawing of the interposer, from theinterposer membrane of FIGS. 30-32.

FIG. 33 d is a right-side-view schematic drawing of the interposer, fromthe interposer membrane of FIGS. 30-32.

FIG. 34 includes 24 specific designs for the interposer supportingmembers, shown in cross-section.

FIG. 35 is a plan drawing of an interposer having supporting membersthat extend between adjacent holes within a particular plane.

FIG. 36 is a plan drawing of an interposer having a supporting planethat completely fills the area between adjacent holes, but is absentabove or below that plane.

FIG. 37 includes 18 specific designs for the interposer, shown incross-section, where the top and bottom contact plates are horizontallyoriented, and the pin direction is generally vertical.

FIG. 38 is a perspective view of an alternate embodiment of a top pin.

FIG. 39 is a top plan view of the subject matter of FIG. 38.

FIG. 40 is a side plan view of the subject matter of FIG. 38.

FIG. 41 is an end plan view of the subject matter of FIG. 38.

FIG. 42 is a perspective view of an alternate embodiment of a top pinhaving a skewed knife edge top surface.

FIG. 43 is a perspective view of an alternate embodiment of a top pinhaving a double sided peaked knife edge top surface.

FIG. 44 is a perspective view of an alternate embodiment of a top pinsimilar to FIG. 43 except having steep sidewall toward the top surface.

FIG. 45 is a perspective view of an alternate embodiment of a top pinhaving a projecting land knife edge top surface.

FIG. 46 is a perspective view of an alternate embodiment of a top pinsimilar to FIG. 45 except the projecting land has a peaked knife edgeatop the land on the top surface.

FIG. 47 is a perspective view of an alternate embodiment of a top pinlike FIG. 46 except the sidewalls of the land are tapered to a sharppeak.

FIG. 48 is a perspective view of an alternate embodiment of a top pinhaving a plurality of lands extending from the pin, in this case withtapered side walls rising to a sharp peak of generally parallelsurfaces.

FIGS. 49-51 are similar to FIG. 48 except they show a top pin having twolands instead of three. FIG. 49, is a perspective view, FIG. 50 is aside view and FIG. 51 is a top view.

FIG. 52 is a perspective view of an alternate embodiment of the lowerpin 30 in FIG. 5.

FIG. 53 is a side plan view of the pin in FIG. 51.

FIG. 54 is a is a perspective view of an alternate embodiment of thelower pin 30 in FIG. 5.

FIG. 55 is a side plan view of the pin in FIG. 54.

FIG. 56 is a bottom plan view of the pin in FIG. 54.

DETAILED DESCRIPTION OF THE DISCLOSURE

Consider an electrical chip that is manufactured to be incorporated intoa larger system. When in use, the chip electrically connects the deviceto the larger system by a series of pins or terminals. For instance, thepins on the electrical chip may plug into corresponding sockets in acomputer, so that the computer circuitry may electrically connect withthe chip circuitry in a predetermined manner. An example of such a chipmay be a memory card or processor for a computer, each of which may beinsertable into a particular slot or socket that makes one or moreelectrical connections with the chip.

It is highly desirable to test these chips before they are shipped, orbefore they are installed into other systems. Such component-leveltesting may help diagnose problems in the manufacturing process, and mayhelp improve system-level yields for systems that incorporate the chips.Therefore, sophisticated test systems have been developed to ensure thatthe circuitry in the chip performs as designed. The chip is attached tothe tester, as a “device under test”, is tested, and is then detachedfrom the tester. In general, it is desirable to perform the attachment,testing, and detachment as rapidly as possible, so that the throughputof the tester may be as high as possible.

The test systems access the chip circuitry through the same pins orterminals that will later be used to connect the chip in its finalapplication. As a result, there are some general requirements for thetest system that perform the testing. In general, the tester shouldestablish electrical contact with the various pins or terminals so thatthe pins are not damaged, and so that a reliable electrical connectionis made with each pin.

Most testers of this type use mechanical contacts between the chip pinsand the tester contacts, rather than soldering and de-soldering or someother attachment method. When the chip is attached to the tester, eachpin on the chip is brought into mechanical and electrical contact with acorresponding pad on the tester. After testing, the chip is removed fromthe tester, and the mechanical and electrical contacts are broken.

In general, it is highly desirable that the chip and the tester bothundergo as little damage as possible during the attachment, testing, anddetachment procedures. Pad layouts on the tester may be designed toreduce or minimize wear or damage to the chip pins. For instance, it isnot desirable to scrape the device I/O (leads, pins, pads or balls),bend or deflect the I/O, or perform any operation that might permanentlychange or damage the I/O in any way. Typically, the testers are designedto leave the chips in a final state that resembles the initial state asclosely as possible. In addition, it is also desirable to avoid orreduce any permanent damage to the tester or tester pads, so that testerparts may last longer before replacement.

There is currently a great deal of effort spent by tester manufacturerson the pad layouts. For instance, the pads may include a spring-loadmechanism that receives the chip pins with a prescribed resisting force.In some applications, the pads may have an optional hard stop at theextreme end of the spring-load force range of travel. The goal of thepad layout is to establish a reliable electrical connection with thecorresponding chip pins, which may be as close as possible to a “closed”circuit when the chip is attached, and may be as close as possible to an“open” circuit when the chip is detached.

Because it is desirable to test these chips as quickly as possible, orsimulate their actual use in a larger system, it may be necessary todrive and/or receive electrical signals from the pins at very highfrequencies. The test frequencies of current-day testers may be up to 40GHz or more, and the test frequencies are likely to increase with futuregeneration testers.

For low-frequency testing, such as that done close to DC (0 Hz), theelectrical performance may be handled rather simplistically: one wouldwant an infinitely high resistance when the chip is detached, and aninfinitesimally small resistance when the chip is attached.

At higher frequencies, other electrical properties come into play,beyond just resistance. Impedance (or, basically, resistance as afunction of frequency) becomes a more proper measure of electricalperformance at these higher frequencies. Impedance may include phaseeffects as well as amplitude effects, and can also incorporate andmathematically describe the effects of resistance, capacitance andinductance in the electrical path. In general, it is desirable that thecontact resistance in the electrical path formed between the chip I/Oand the corresponding pad on the load card be sufficiently low, whichmaintains a target impedance of 50 ohms, so that the tester itself doesnot significantly distort the electrical performance of the chip undertest. Note that most test equipment is designed to have 50 ohm input andoutput impedances.

For modern-day chips that have many, many closely spaced I/O, it becomeshelpful to simulate the electrical and mechanical performance at thedevice I/O interface. Finite-element modeling in two-or three dimensionshas become a tool of choice for many designers. In some applications,once a basic geometry style has been chosen for the tester padconfiguration, the electrical performance of the pad configuration issimulated, and then the specific sizes and shapes may be iterativelytweaked until a desired electrical performance is achieved. For theseapplications, the mechanical performance may be determined almost as anafterthought, once the simulated electrical performance has reached aparticular threshold.

A general summary of the disclosure follows.

The terminals of a device under test are temporarily electricallyconnected to corresponding contact pads on a load board by a series ofelectrically conductive pin pairs. The pin pairs are held in place by aninterposer membrane that includes a top contact plate facing the deviceunder test, a bottom contact plate facing the load board, and avertically resilient, non-conductive member between the top and bottomcontact plates. Each pin pair includes a top and bottom pin, whichextend beyond the top and bottom contact plates, respectively, towardthe device under test and the load board, respectively. The top andbottom pins contact each other at an interface that is inclined withrespect to the membrane surface normal. When compressed longitudinally,the pins translate toward each other by sliding along the interface. Thesliding is largely longitudinal, with a small and desirable lateralcomponent determined by the inclination of the interface. The interfacemay optionally be curved along one or two dimensions, optionally withdifferent curvatures and/or concavities in each direction, and mayoptionally include one or more locating features, such as a ridge orgroove. The top and bottom contact plates may be made from a polyimideor non-conductive, flexible material, such as KAPTON®, which iscommercially available from the DuPont Corporation. Another examplematerial is polyetheretherketone (PEEK), an engineering plasticcommercially available from manufacturers such as Victrex. The materialbetween the contact plates may be a foam or elastomeric material. Thepins in each pair may optionally be made from different metals.

The preceding paragraph is merely a summary of the disclosure, andshould not be construed as limiting in any way. The test device isdescribed in much greater detail below.

FIG. 1 is a side-view drawing of a portion of the test equipment forreceiving a device under test (DUT) 1. The DUT 1 is placed onto thetester 5, electrical testing is performed, and the DUT 1 is then removedfrom the tester 5. Any electrical connections are made by pressingcomponents into electrical contact with other components; there is nosoldering or de-soldering at any point in the testing of the DUT 1.

The entire electrical test procedure may only last about a fraction of asecond, so that rapid, accurate placement of the device under test 1becomes important for ensuring that the test equipment is usedefficiently. The high throughput of the tester 5 usually requiresrobotic handling of the devices under test 1. In most cases, anautomated mechanical system places the DUT 1 onto the tester 5 prior totesting, and removes the DUT 1 once testing has been completed. Thehandling and placement mechanism may use mechanical and optical sensorsto monitor the position of the DUT 1, and a combination of translationand rotation actuators to align and place the DUT 1 on the testbed. Suchautomated mechanical systems are mature and have been used in many knownelectrical testers; these known robotic systems may also be used withany or all of the tester elements disclosed herein. Alternatively, theDUT 1 may be placed by hand, or placed by a combination of hand-fed andautomated equipment.

Likewise, the electrical algorithms that are used to test each terminalon the DUT 1 are well established, and have been used in many knownelectrical testers. These known electrical algorithms may also be usedwith any or all of the tester elements disclosed herein.

The device under test 1 typically includes one or more chips, andincludes signal and power terminals that connect to the chip. The chipand terminals may be on one side of the device under test 1, or may beon both sides of the device under test 1. For use in the tester 5, allthe terminals 2 should be accessible from one side of the device undertest 1, although it will be understood that there may be one or moreelements on the opposite side of the device under test 1, or that theremay be other elements and/or terminals on the opposite side that may notbe tested by accessing terminals 2.

Each terminal 2 is formed as a small, generally spherical ball ofsolder. Prior to testing, the ball 2 is attached to an electrical leadthat connects internally to other leads, to other electrical components,and/or to one or more chips on the device under test 1. The volume andsize of the solder balls may be controlled quite precisely, and there istypically not much difficulty caused by ball-to-ball size variations orplacement variations. During testing, the terminals 2 remain solid, andthere is no melting or re-flowing of any solder balls 2.

The terminals 2 may be laid out in any suitable pattern on the surfaceof the device under test 1. In some cases, the terminals 2 may be in agenerally square grid, which is the origin of an expression thatdescribes the device under test 1, “ball grid array”. There may also bedeviations away from a rectangular grid, including irregular spacingsand geometries. It will be understood that the specific locations of theterminals may vary as needed, with corresponding locations of pads onthe load board and pin pairs on the membrane being chosen to match thoseof the device under test terminals 2. In general, the spacing betweenadjacent terminals 2 is in the range of 0.25 to 1.5 mm, with the spacingbeing commonly referred to as a “pitch”.

When viewed from the side, as in FIG. 1, the device under test 1displays a line of terminals 2, which may optionally include gaps andirregular spacings. These terminals 2 are made to be generally planar,or as planar as possible with typical manufacturing processes. In manycases, if there are chips or other elements on the device under test 1,the protrusion of the chips is usually less than the protrusion of theterminals 2 away from the device under test 1.

The tester 5 of FIG. 1 includes a load board 3.

The load board 3 includes a load board substrate 6 and circuitry that isused to test electrically the device under test 1. Such circuitry mayinclude driving electronics that can produce one or more AC voltageshaving one or more particular frequencies, and detection electronicsthat can sense the response of the device under test 1 to such drivingvoltages. The sensing may include detection of a current and/or voltageat one or more frequencies. Such driving and sensing electronics is wellknown in the industry, and any suitable electronics from known testersmay be used with the tester elements disclosed herein.

In general, it is highly desirable that the features on the load board3, when mounted, are aligned with corresponding features on the deviceunder test 1. Typically, both the device under test 1 and the load board3 are mechanically aligned to one or more locating features on thetester 3. The load board 3 may include one or more mechanical locatingfeatures, such as fiducials or precisely-located holes and/or edges,which ensure that the load board 3 may be precisely seated on the tester5. These locating features typically ensure a lateral alignment (x, y)of the load board, and/or a longitudinal alignment (z) as well. Themechanical locating features are well known in the industry, and anysuitable electronics from known testers may be used with the testerelements disclosed herein. The mechanical locating features are notshown in FIG. 1.

In general, the load board 3 may be a relatively complex and expensivedevice. In many cases, it may be advantageous to introduce anadditional, relatively inexpensive element into the tester 5 thatprotects the contact pads 4 of the load board 3 from wear and damage.Such an additional element may be an interposer membrane 10. Theinterposer membrane 10 also mechanically aligns with the tester 3 withsuitable locating features (not shown), and resides in the tester 5above the load board 3, facing the device under test 1.

The interposer membrane 10 includes a series of electrically conductivepin pairs 20, 30. In general, each pin pair connects one contact pad 4on the load board 3 to one terminal 2 on the device under test 1,although there may be testing schemes in which multiple contact pads 4connect to a single terminal 2, or multiple terminals 2 connect to asingle contact pad 4. For simplicity, we assume in the text and drawingsthat a single pin pair connects a single pad to a single terminal,although it will be understood that any of the tester elements disclosedherein may be used to connect multiple contact pads connect to a singleterminal, or multiple terminals to a single contact pad. Typically, theinterposer membrane 10 electrically connects the load board pads and thebottom contact surface of the test contactor. It may alternatively beused to convert an existing load board pad configuration to a vehicle,which is a test socket used to connect and test a device under test.

Although the interposer membrane 10 may be removed and replacedrelatively easily, compared with removal and replacement of the loadboard 3, we consider the interposer membrane 10 to be part of the tester5 for this document. During operation, the tester 5 includes the loadboard 3, the interposer membrane 10, and the mechanical constructionthat mounts them and holds them in place (not shown). Each device undertest 1 is placed against the tester 5, is tested electrically, and isremoved from the tester.

A single interposer membrane 10 may test many devices under test 1before it wears out, and may typically last for several thousand testsor more before requiring replacement. In general, it is desirable thatreplacement of the interposer membrane 10 be relatively fast and simple,so that the tester 5 experiences only a small amount of down time formembrane replacement. In some cases, the speed of replacement for theinterposer membrane 10 may even be more important than the actual costof each membrane 10, with an increase in tester up-time resulting in asuitable cost savings during operation.

FIG. 1 shows the relationship between the tester 5 and the devices undertest 1. When each device 1 is tested, it is placed into a suitablerobotic handler with sufficiently accurate placement characteristics, sothat a particular terminal 2 on the device 1 may be accurately andreliably placed (in x, y and z) with respect to corresponding pin pairs20, 30 on the interposer membrane 10 and corresponding contact pads 4 onthe load board 3.

The robotic handler (not shown) forces each device under test 1 intocontact with the tester 5. The magnitude of the force depends on theexact configuration of the test, including the number of terminals 2being tested, the force to be used for each terminal, typicalmanufacturing and alignment tolerances, and so forth. In general, theforce is applied by the mechanical handler of the tester (not shown),acting on the device under test 1. In general, the force is generallylongitudinal, and is generally parallel to a surface normal of the loadboard 3.

FIG. 2 shows the tester and device under test 1 in contact, withsufficient force being applied to the device under test 1 to engage thepin pairs 20, 30 and form an electrical connection 9 between eachterminal 2 and its corresponding contact pad 4 on the load board 3. Asstated above, there may alternatively be testing schemes in whichmultiple terminals 2 connect to a single contact pad 4, or multiplecontact pads 4 connect to a single terminal 2, but for simplicity in thedrawings we assume that a single terminal 2 connects uniquely to asingle contact pad 4.

FIGS. 3 and 4 are side-view cross-sectional drawings of an exemplaryinterposer membrane 10 in its relaxed and compressed states,respectively. In its relaxed state, there is no electrical connectionbetween terminal 2 on the device under test 1 and contact pad 4 on theload board 3. In its compressed state, in which the device under test 1is forced toward the load board 3, there is an electrical connection 9between terminal 2 on the device under test 1 and contact pad 4 on theload board 3.

In some cases, the interposer membrane 10 may extend across essentiallythe entire lateral extent of the load board, or at least over thelateral area subtended by the load board contact pads 4. The membrane 10includes a sandwich structure that mechanically supports electricallyconductive pin pairs, with each pin pair corresponding to a terminal 2on the device under test 1 and a contact pad 4 on the load board 3. Thesandwich structure is described below, followed by a detaileddescription of the pin pairs.

The membrane 10 may be formed as a sandwich structure, with aninterposer 50 being surrounded by a top contact plate 40 and a bottomcontact plate 60. In some cases, the layers 40, 50, 60 of the membrane10 are held together by relatively thin layers of adhesive 41, 61.

The interposer 50 is an electrically insulating, vertically resilientmaterial, such as foam or an elastomer. When the device under test isforced toward the load board, the interposer 50 compresses in thelongitudinal (vertical) direction, as is the case in FIG. 4. Thevertical compression is generally elastic. When the device under test isreleased, the interposer 50 expands in the longitudinal (vertical)direction to its original size and shape, as is the case in FIG. 3.

Note that there may optionally be some transverse (horizontal)compression as well, although the transverse component is generallysmaller than the longitudinal component. In general, the interposer 50material does not substantially “flow” laterally when a longitudinalforce is applied. In some cases, there may be a resisting lateral forcesupplied by the interposer 50 material, which can help constrain thepair of pins 20, 30 to a particular columnar volume and prevent orreduce any lateral spreading of the overlapping portions of the pins ineach pair.

On either side of the interposer 50 is a contact plate, with a topcontact plate 40 facing the device under test 1 and a bottom contactplate 60 facing the load board 3. The contact plates 40, 60 may be madefrom an electrically insulating, flexible material, such as a polyimideor KAPTON®. Alternatively, the contact plates 40, 60 may be made fromany semi-rigid thin film material, which can include a polyester, apolyimide, PEEK, KAPTON®, nylon, or any other suitable material. In somecases, the contact plates 40, 60 are adhered to the interposer 50 by anadhesive 41, 61. In other cases, the contact plates 40, 60 are madeintegral with the interposer 50. In still other cases, the contactplates 40, 60 are free floating and not physically attached to theinterposer 50, which may allow for quick removal and replacement. Forthese cases, there is no adhesive 41, 61 that binds the interposer 50 tothe contact plates 40, 60.

The contact plates 40, 60 (KAPTON®) are structurally stronger than theinterposer 50 (foam), and provide a durable exterior to the interposermembrane 10. In addition, they deform less than the interposer 50 whenthe device under test 1 is forced toward the load board 3. Note that inFIG. 4, the top contact plate 40 may bend longitudinally to accommodatethe longitudinal compression, but the material that actually compressesis the foam or elastomer of the interposer 50. In other words, duringcompression, the top and bottom contact plate 40, 60 may be pushedtoward each other and one or both may longitudinally deform, but neitherone significantly compresses or changes thickness.

A membrane 10 that uses KAPTON® contact plates 40, 60 may have severaladvantages.

First, it is easy and relatively inexpensive to cut and place holes intothe semi-rigid film, which may be made from a material such as KAPTON®.As a result, once the lateral locations of the contact pads 4 and thecorresponding terminals 2 are determined (usually by the manufacturer ofthe device under test 1), the locations and sizes may be fed into amachine that drills or etches the holes in the desired locations. Notethat the machining/processing of KAPTON® is far less expensive forcomparable processing of a metallic layer.

Second, after machining, the KAPTON® layers are very strong, and resistlateral deformation of the hole shapes or locations. As a result, theKAPTON® layers themselves may be used to determine the lateral locationsof the pin pairs, during assembly of the interposer membrane 10. Inother words, the pins may be inserted into the existing holes in theKAPTON®, eliminating the need for an additional, expensive tool toprecisely place the pins in (x, y).

The exemplary membrane 10 shown in FIG. 3 shows the top pin 20 andbottom pin 30 as being spatially separated when the membrane 10 is inits relaxed state. When the membrane 10 is compressed, as in FIG. 4, thetop pin 20 and bottom pin 30 are brought into physical and electricalcontact.

Note that having a pin separation in the relaxed state is optional.Alternatively, the top and bottom pins may be in physical and electricalcontact even when the membrane is in its relaxed state; this is the caseof the design discussed below with reference to FIGS. 5 and 6.

Having discussed the sandwich structure of the interposer membrane 10,we turn now to the top pin 20 and bottom pin 30.

The top pin 20, also known as a slider pin 20, has a top contact pad 21that extends generally laterally around the pin 20 and comes intocontact with the terminal 2 on the device under test 1. This lateralextension makes the top contact pad 21 a “larger target” for theterminal 2 during testing, and helps relax some fabrication andalignment tolerances on all the tester and device elements. The topcontact pad 21 need not be flat or rectangular in profile; other optionsare discussed below with reference to FIGS. 12-18.

The top pin 20 has a longitudinal member 22 that extends away from thetop contact pad 21 toward the load board 3. In some cases, thelongitudinal member 22 may include all of the top pin 20 except the topcontact pad 21.

The longitudinal member 22 may include at least one mating surface 23.The mating surface 23 is shaped to contact an analogous mating surface33 on the bottom pin 30 during longitudinal compression of the pin pair,so that the mating surfaces 23 and 33 on the pin pair provide goodmechanical and electrical contact between the top and bottom pins. Here,the element numbers “23” and “33” refer to general mating surfaces. Thesurfaces themselves may take on many shapes and orientations, andspecific shapes are labeled in the drawings as “23A”, “33A”, “23B”,“33B”, and so forth. FIGS. 3 and 4 show flat mating surfaces 23A and33A. Some other suitable shapes are shown below in subsequent drawings.

The bottom pin 30, also known as a base pin 30, has a bottom contact pad31, a longitudinal member 32 and a mating surface 33A, all of which aresimilar in construction to the analogous structures in the top pin 20.

In some cases, the top and bottom pins are formed from different metals,so that the pins avoid “sticking” together over the course of repeatedcontact along the mating surfaces 23A and 33A. Examples of suitablemetals include copper, gold, solder, brass, silver, and aluminum, aswell as combinations and/or alloys of the above conductive metals.

In the exemplary design of FIGS. 3 and 4, the mating surfaces 23A and33A are essentially planar. When brought together, the mating surfaces23A and 33A form a so-called virtual “interface surface” 70A, which inthis example is a plane. Other examples are provided below.

Note that the hole in the membrane 10, and likewise the cross-section ofthe longitudinal members 22 and 32, may be circular, elliptical,elongated, rectangular, square, or any other suitable shape. In all ofthese cases, the membrane 10 holds the top and bottom pins together, ina manner similar to having a rubber band around the pins' circumferencein the vicinity of their overlapping longitudinal portions. The membrane10 provides resistance to motion in the lateral direction.

Whereas the interface surface 70A of FIGS. 3 and 4 is generally planar,the interface surface may alternatively take on other shapes. Forinstance, the interface surface 70B in FIGS. 5 and 6 is curved. The toppin mating surface 23B is convex, and the bottom pin mating surface 33Bis concave, with both having the same radius of curvature so that theyfit together.

In FIG. 5, when the membrane is in its relaxed state, the top pin 20 andbottom pin 30 have generally parallel longitudinal members. In FIG. 6,when the device under test is forced against the load board, the top pin20 has slid along the curved interface surface 70B, thereby translatingthe top pin 20 downward and pivoting the top pin 20 so that the topcontact pad is inclined with respect to the terminal 2 on the deviceunder test, and the top pin longitudinal member is inclined with respectto the bottom pin longitudinal member.

This angular incline may be useful. Note in FIG. 6 that when theelectrical connection 9 is made between the terminal (ball) 2 and theload board contact pad 4, that the top contact pad 21 on the top pin 20contacts the ball 2 away from the center of the ball 2. This shift incontact area may cause a desirable “wiping” function, in which the topcontact pad 21 on the top pin 20 can break through any oxide layers thathave formed on the solder ball 2. This, in turn, may result in animproved electrical connection between the ball 2 and the top contactpad 21 of the top pin 20.

In addition, depending on the location of the center of rotation of theinterface surface 70B, there may be an additional lateral translation ofthe top pin 20 as the device under test is forced against the loadboard. Generally, this lateral (x, y) translation is smaller than thelongitudinal (z) translation of the top pin, but is desirablenonetheless because it may also cause the “wiping” function describedabove.

Note that this lateral translation is also present on the designs ofFIGS. 3 and 4, in which the interface surface 70A is planar, and isinclined away from a surface normal of the interposer membrane 10. As aresult, the designs of FIGS. 3 and 4 display the desirable “wiping”function described above.

Note also that while “wiping” may be desirable for the solder ballterminals 2 on the devices under test, “wiping” is typically notdesirable for the contact pads 4 on the load board 3. In general,persistent and repeated wiping of the load board contact pads 4 may leadto deterioration of the pads themselves, and may eventually lead tofailure of the load board 3, which is highly undesirable. For thedesigns considered herein, the top pin 20 is the pin that moves andperforms the wiping, while the bottom pin 30 remains generallystationary, and does not wipe against the load board contact pad 4.

Note that the top pin 20 has a top relief surface 24, which is cut awayfrom the top pin longitudinal member so that the top pin may pivotwithout bumping into the resilient membrane (not shown—on the leftportion of FIG. 6). In some cases, when the top pin 20 is at fullcompression, as in FIG. 6, the top relief surface 24 is perpendicular tothe plane of the interposer membrane 10. In the case shown in FIG. 6,the bottom pin 30 includes a bottom relief surface 34 that isperpendicular to the membrane surface, which does not cause anyinterference with the membrane foam because the bottom pin 30 generallydoes not pivot.

FIGS. 3 and 4 showed a planar interface surface 70A, and FIGS. 5 and 6showed a curved interface surface 70B. These and other configurationsare shown more clearly in FIGS. 7 through 11.

FIG. 7 is a plan drawing of the planar interface surface 70A shown inFIG. 3.

Note that the plane itself is inclined with respect to the surfacenormal of the interposer membrane 10. In other words, the plane is nottruly vertical, but is inclined away from vertical by an angle, such as1 degree, 5 degree, 10 degrees, 15 degrees, 20 degrees, or an anglewithin a range of angles, such as 1-30 degrees, 5-30 degrees, 10-30degrees, 15-30 degrees, 20-30 degrees, 5-10 degrees, 5-15 degrees, 5-20degrees, 5-25 degrees, 10-15 degrees, 10-20 degrees, 10-25 degrees,15-20 degrees, 15-25 degrees, or 20-25 degrees. To form this planarinterface surface 70A, top pin mating surface 23A and bottom pin matingsurface 33A are both planar.

With a planar interface surface 70A, there is no restriction of movementof the top mating surface 23A with respect to the bottom mating surface33A. The mating surfaces are free to translate and rotate with respectto each other while remaining in contact with each other.

FIG. 8 is a plan drawing of the curved interface surface 70B shown inFIG. 5. In this case, the curvature is only along one dimension, so thatthe interface surface 70B assumes a cylindrical profile. There iscurvature along a vertical direction, but no curvature along ahorizontal direction. To form this cylindrically curved interfacesurface 70B, the top pin mating surface 23B is cylindrically curved andconvex, and the bottom pin mating surface 33B is cylindrically curvedand concave. Each mating surface has the same radius of curvature. Notethat in other cases, the concavity may be reversed, so that the top pinmating surface 23B is concave and the bottom pin mating surface 33B isconvex.

The curved interface surface 70B does restrict movement of the pins withrespect to each other. The mating surfaces of the pins may translatehorizontally, along the dimension that has no curvature, and may pivotabout the center of curvature (the mating surfaces and interface surfaceall have the same center of curvature), but may not translate verticallywithout rotation with respect to each other.

The placement of the center of curvature does determine the amount ofrotation and/or lateral translation one may achieve for a givenlongitudinal translation of the pins. In general, it is desirable tohave enough translation and/or rotation to provide adequate “wiping” ofthe ball terminal 2, as described above.

FIG. 9 is a plan drawing of a curved interface surface 70C that hascurvature in both horizontal and vertical directions. In someapplications, the horizontal and vertical radii of curvature are thesame, meaning that the interface surface 70C is spherically curved. Thisis the case as drawn in FIG. 9. In other applications, the horizontaland vertical radii of curvature are different, meaning that theinterface surface has a single concavity but a more complex shape.

FIG. 10 is a plan drawing of a saddle-shaped interface surface 70D, inwhich the vertical and horizontal curvatures have opposite concavity.Note that the top pin mating surface and the bottom pin mating surfaceare both saddle-shaped, with surface profiles that are mated to form theinterface surface 70D.

Finally, FIG. 11 is a plan drawing of an interface surface 70E having alocating feature, such as a groove or ridge. Note that the matingsurface of one pin may have a groove, while the mating surface of theother pin has the complementary feature of a ridge that fits into thegroove. Such a locating feature may restrict motion along a particulardimension or axis. As drawn in FIG. 11, the only possible relativemotion of the mating surfaces is a largely vertical pivoting around thecenter of curvature; no horizontal relative motion is allowed by thelocating feature.

Other suitable shapes, radii of curvature, concavity, and/or locatingfeatures are certainly possible, in addition to those shown in FIGS. 7through 11. In each case, the top pin mating surface and bottom pinmating surface have complementary features, which may optionallyrestrict motion in a particular dimension or rotation along a particulardirection. During use of the pins during testing, the compression of thepins retains intimate contact between the mating surfaces, and thecontact is along the interface surface.

The top contact pad 21 can include any of a variety of features that mayhelp enhance electrical contact with the ball terminal 2 on the deviceunder test 1. Several of these are shown in FIGS. 12-18.

FIG. 12 is a plan drawing of a generally planar top contact pad 21A.

FIG. 13 is a plan drawing of a top contact pad 21B that extends out ofthe plane of the pad. In the example shown in FIG. 13, the center of thecontact pad 21B extends farther away from the top pin than the edges do,although this is not a requirement. In some cases, the top contact pad21B is curved and is convex.

FIG. 14 is a plan drawing of a top contact pad 21C that includes aprotrusion out of the plane of the pad. In the example shown in FIG. 14,the protrusion is essentially a line that extends through the center ofthe pad. In other cases, the line may be perpendicular to the one drawnin FIG. 14. In still other cases, the protrusion may be a point orprotruding region, rather than a line. Alternatively, other protrusionshapes and orientations are possible. In some cases, the top contact pad21C is curved and is concave. In other cases, the top contact pad 21Cincludes both concave and convex portions.

FIG. 15 is a plan drawing of a top contact pad 21D that includesmultiple protrusions out of the plane of the pad. In the example shownin FIG. 14, the protrusions are essentially linear and parallel,although other shapes and orientations may also be used. In some cases,the top contact pad 21D includes only flat portions. In other cases, thetop contact pad 21D includes both curved and flat portions. In somecases, the top contact pad 21D includes one or more edges or blades,which may be useful for the “wiping” action described above.

FIG. 16 is a plan drawing of an inclined top contact pad 21E. Onepossible advantage of having an inclination to the top contact pad isthat it may encourage “wiping” of the terminal 2.

FIG. 17 is a plan drawing of an inclined top contact pad 21F withmultiple protrusions out of the plane of the pad. In addition to theinclination, the protrusions may also enhance “wiping” of the terminal2. Here, the protrusions are grooves or ridges that are parallel to thedirection of the ball wiping action. Alternatively, the grooves may beperpendicular to the ball wiping action, as in FIG. 15.

FIG. 18 is a plan drawing of a textured top contact pad 21G. In somecase, the texture is a series of repeating structures, which may beuseful for “wiping” the terminal 2. In some cases, the top contact pad21G is knurled. In some cases, the knurl or texture may be superimposedon a curved or otherwise shaped top contact pad.

FIG. 19 is a plan drawing of a radially enlarged top contact pad 21H. Inpractice, the maximum size that may be used may depend on thetwo-dimensional layout of the pins on the devices under test 1, themechanical response of the interposer membrane (i.e., will the membranelongitudinally distort enough to ensure good contact between top andbottom pins), and so forth. In some cases, the shape or footprint of thetop contact pad may be round, elliptical, skewed, rectangular,polygonal, square, or any other suitable shape. Furthermore, the topcontact pad may have an enlarged footprint in combination with any ofthe inclinations, protrusions and textures described above.

FIG. 20 is a side-view drawing of a top pin 20 with a top contact pad 21that has rounded edges 25. In general, any or all of the edges in thetop pin 20, and likewise, the bottom pin 30, may be rounded or sharp.Any rounded edges may be used with any or all of the pin features shownherein.

It should be noted that any combination of the features shown in FIGS.12-20 may be used simultaneously. For instance, there may be a generallyflat top pin contact pad (21A) that also has grooves in the lengthdimension (21F), or a top pin extending out of the plane (21B) that alsohas grooves in the length dimension (21F) and rounded edges (25). Any orall of these features may be mixed and matched as needed.

The top pin 20 and bottom pin 30 may optionally include one or morefeatures that can allow the pins to be snapped into the interposermembrane 10. Some exemplary engagement and/or retention features areshown in FIG. 21-24.

FIG. 21 is a side-view cross-sectional drawing of a top pin 20 having atop pin engagement feature 26A on one side. In this case, the engagementfeature is a horizontal depression, or lip, running along the undersideof the top contact pad. Note that in some cases, the longitudinal memberof the top pin is rectangular in profile, and the lip may run along one,two, three or all four edges of the top pin. When inserted into the holein the interposer membrane, the top pin engagement feature 26A mayengage all or a part of the top contact plate 40, and may optionallyengage a portion of the foam or elastomer interposer 50. Such engagementallows the top pin 20 to be connected to the rest of the interposermembrane without adhesives and without any additional connectioncomponents. Additionally, such an engagement feature 26A may allow theinterposer membrane to be assembled by first having the sandwichstructure of the top plate, the foam and the bottom plates, with holesin the locations that will ultimately house pins, then by inserting eachpin into a hole until the engagement feature catches the KAPTON® contactplate. Each hole itself should be suitably sized to allow the pin to besnugly inserted up to the lip, albeit with a tight fit.

FIG. 22 is a side-view cross-sectional drawing of a top pin 20 having atop pin engagement feature 26B on two opposing sides. This has theadvantages of feature 26A shown in FIG. 21, with additional engagementand retention strength. For top pin longitudinal members that have around cross-section, the lip 26B may extend all or partway around thecircumference of the longitudinal member.

FIG. 23 is a side-view cross-sectional drawing of a top pin 20 having atwo top pin engagement features 26B engaging the top contact plate, andone engagement feature 26C engaging the foam interposer 50. This alsohas additional engagement and retention strength. In some cases, it maybe preferable to engage the bottom plate to the foam, rather than thetop plate, so that the top plate is free to move without restriction. Insome cases, the foam may not fully extend into the engagement feature,or may not extend at all into the engagement feature.

The bottom pin 30 may also have similar engagement and retentionfeatures. For instance, FIG. 24 shows an engagement feature or lip 36Athat engages a portion of the bottom contact plate 60. Otherconfigurations are possible, analogous to those for the top pin 20.

Several of the figures above show individual features or elements. FIGS.25 through 27 show a more detailed example, in which many of thefeatures are combined. Note that this is merely an example and shouldnot be construed as limiting in any way.

FIG. 25 is a perspective-view cross-sectional drawing of an exemplaryinterposer membrane 10. FIG. 26 is an end-on cross-sectional drawing ofthe interposer membrane 10 of FIG. 25. FIG. 27 is a plan drawing of theinterposer membrane 10 of FIGS. 25 and 26.

The terminals from a device under test contact respective top pins 20,and the contact pads 4 from a load board contact respective bottom pins30. In this example, the top contact pad 21B is cylindrically curved andconvex, and the bottom contact pad 31 is flat. The top and bottomcontact pins slide past each other along mating surfaces 23B and 33B,which in this example are cylindrically curved. The mating surfaces 23Band 33B contact each other along a virtual, cylindrically curvedinterface surface 30B, denoted by the dashed line in FIG. 26. The pinshave top and bottom relief surfaces 24, 34, which in this example areboth oriented generally perpendicular to the membrane 10 when the pinsare fully compressed. In this example, the top and bottom pin contactpads have rounded edges 25, 35. The top and bottom pins have engagementfeatures 26A, 36A that engage the top and bottom contact plates, 40, 60,respectively, as well as optional engagement features 26C, 36C thatengage the foam layer 50.

FIG. 27 shows an exemplary layout for the pins 20 in the membrane 10. Inthis example, the pins themselves are laid out in a generally squaregrid, corresponding to both the terminal and contact pad layouts of thedevice under test and the load board, respectively. Note that thefootprint of the contact pad is oriented at a 45 degree angle withrespect to the square grid, which allows for a larger contact pad thanwould be possible if the pad were extended along the square grid itself.Note also that the orientation of the interface surface 70B is at a 45degree angle with respect to the square grid. In practice, the interfacesurface 70B may alternatively be oriented along the grid, or at anysuitable angle with respect to the grid.

It is instructive to consider some elements that are particularly usefulfor so-called “Kelvin” testing. Unlike the one terminal/one contact padtesting described above, Kelvin testing measures the resistance betweentwo terminals on the device under test. The physics of such ameasurement is straightforward—we pass a known current (I) between thetwo terminals, measure the voltage difference (V) between the twoterminals, and use Ohm's Law (V=IR) to calculate the resistance (R)between the two terminals.

In a practical implementation, each terminal on the device under test iselectrically connected to two contact pads on the load board. Onecontact pad is effectively a current source or current sink, whichsupplies or receives a known amount of current. The other contact padacts effectively as a voltmeter, measuring a voltage but not receivingor supplying a significant amount of current. In this manner, for eachterminal on the device under test, one pad deals with I and the otherdeals with V.

While it is possible to use two separate pin pairs for each terminal,each pin pair corresponding to a single contact pad on the load board,there are drawbacks to this method. For instance, the tester would haveto make two reliable electrical connections at each terminal, whichwould prove difficult for exceedingly small or closely spaced terminals.In addition, the membrane that holds the pin pairs would includeessentially twice as many mechanical parts, which may increase thecomplexity and cost of such a membrane.

A better alternative is a pin mechanism that combines the electricalsignals from two contact pads on the load board internally, so that onlyone top pin pad need make reliable contact with each terminal, ratherthan two distinct pins contacting each terminal. There are five possiblepin schemes that can combine the two load board signals into a singletop pin, each described briefly below.

First, the electrical signals are combined at the load board itself, asis the case for a single bottom contact pad that subtends two adjacentpads on the load board.

Second, the electrical signals are combined at the bottom pin. For thiscase, the membrane would include two distinct bottom contact pads, or asingle bottom contact pad with an insulating portion that electricallyseparates one load board contact pad from the other.

Third, the electrical signals are combined at the top pin. For thiscase, the entire bottom pin is divided into two halves separated by anelectrical insulator.

Fourth, the electrical signals are combined at the top contact pad, orequivalently, as close as possible to the terminal of the device undertest. For this case, the entire bottom pin and much or all of thelongitudinal member of the top pin are divided into two halves separatedby an electrical insulator. The halves are electrically joined at thetop contact pad, and are electrically isolated from each other below thetop contact pad, i.e., between the top contact pad and the respectiveload board contact pad.

Finally, fifth, the electrical signals are combined only at the terminalof the device under test. The top contact pad, the top pin, the bottompin, and the bottom contact pad(s) all include an electrical insulatorthat divides the pins and pad(s) into two electrically conductiveportions that are electrically insulated from each other. In practicalterms, the pins may be symmetrically bisected by the insulatingmaterial, so that a “left” half may be electrically insulated from a“right” half, where the “left” half electrically contacts one pad on theload board and the “right” half electrically contacts another pad on theload board.

In some cases, there are advantages to keeping the electrical signalsisolated from each other along most or all of the longitudinal extent ofthe pins. If the signals are connected at the load board, there is anunnecessary redundancy, as if there were to two independent signalpaths. In addition, connecting the signals at the load board mayactually lower the associated inductances, since two inductances inparallel result in half the inductance.

An example of the fifth case above is shown in FIGS. 28 and 29.

FIG. 28 is a plan drawing of an exemplary top contact pad 121 for Kelvintesting, with an insulating portion 128 that separates the twoconducting halves 127, 129 of the pad. In many cases, the insulatingportion extends throughout the full longitudinal extent of the top pin,and effectively separates the pin into two conducting portions that areelectrically insulated from each other. In many cases, the bottom pinmay also include an analogous insulating portion that separates thebottom pin into two conducting portions that are electrically insulatedfrom each other.

FIG. 29 is a side-view drawing of an exemplary pin pair 120, 130 forKelvin testing, with an insulating ridge 180 that extends outward fromthe top pin mating surface 123. The ridge 180 may be generally planarand may extend through the entire top pin 120. The ridge 180 effectivelybisects the top pin 120, and electrically insulates one half (facing theviewer in FIG. 29) from the other half (facing away from the viewer inFIG. 29). The ridge may be made from any suitable insulating material,such as KAPTON®, and so forth.

The ridge 180 itself extends outward from the mating surface 123, andelectrically insulates one half of the surface from the other. Themating surface 123 now includes two non-contiguous halves, separated bya ridge that extends outwardly from the surface. The correspondingmating surface 133 on the bottom pin 130 includes a suitable groove foraccepting the ridge; the groove is an indentation along the matingsurface 133 and is not shown in FIG. 29. In some cases, the groove mayextend deeper than the ridge, so the “top” of the ridge does not contactthe “bottom” of the groove at any point in the range of travel. This maybe desirable, in that the mating surfaces 123 and 133 may share lesscommon surface area, and may produce less friction as they move pasteach other. In other cases, the “top” of the ridge does contact the“bottom” of the groove. The ridge and groove structure serves to keepthe mating surfaces aligned, as with the cases described above.

In some cases, the groove and ridge are both made from electricallyinsulating material, which separate the top and bottom pins each intotwo conducting portions that are electrically insulated from each other.This allows a single mechanical pin to be used for two independentelectrical contacts, which is beneficial for Kelvin testing. Note thatin FIG. 29, the groove on the bottom pin is hidden by surface 133, andwould appear to the right of surface 133, much in the way that ridge 180appears to the right of surface 123 in the top pin. The groove may be asdeep or deeper than the ridge 180.

In some cases, the groove (not shown) would be sized to receive theridge or land 180 and just wider than the ridge. With this sizing, theelements can slide by each other freely. In addition, the ridge-grooveengagement provides a reliable track for sliding of the top and bottomelements 120, 130, thereby preventing skew or misalignment as theelements move with respect to each other. It is also possible to makethe ridge and groove of an electrically conductive material (i.e., not adielectric) where Kelvin testing capabilities are not needed. This mayprovide the same tracking capability and may also increase theelectrical contact surface area.

The virtual interface surface 170 may differ slightly from the casesdescribed above, in that it may not include the portion occupied by theridge and groove structure. In these cases, the interface surface 170may include two non-contiguous regions, one in the “front” and one inthe “back”, as drawn in FIG. 29. Each region may include planar, acylindrically curved, or a spherically curved surface, as describedabove.

Note that in some cases, the interface surface may includediscontinuities, such as a change in the radius of curvature. Ingeneral, such discontinuities are perfectly acceptable as long as thetwo mating surfaces 123 and 133 remain in contact for most or all oftheir full ranges of travel. For instance, the “front” portion may haveone particular radius of curvature, and the “rear” portion may have adifferent radius of curvature, and the two centers of curvature may becoincident or collinear, to permit the mating surfaces to move andremain in contact. Other variations may include “stripes” along themating surfaces, where each stripe may have its own particular radius ofcurvature, the radii all being coincident or collinear.

It will be understood that the ridge and groove of the top and bottompins may be exchanged for a groove and ridge on the top and bottom pins,respectively. It will also be understood that the concavities of the topand bottom mating surfaces may be reversed as well.

Note that in the text and figures thus far, the membrane 10 has beenshown as a sandwich structure, with two outer layers surrounding aninner layer. In general, the outer layers of this sandwich structurehave different mechanical properties than the inner layer, with theouter layers being a semi-rigid thin film and the inner layer being avertically resilient material. As an alternative, the sandwich structuremay be replaced by a monolithic membrane, which may be formed as asingle layer having a single set of mechanical properties. The outersurfaces of such a single monolithic layer would face the load board anddevice under test. In such cases, the membrane itself may be formed as asingle layer having a set of vertically-oriented holes. The two pins areplaced into the holes from the top and bottom.

Finally, we describe the interposer 50 in more detail.

The simplest design for the interposer is just a monolithic structure,with holes extending from the top contact plate to the bottom contactplate that can accommodate the pins. In this simplest design, theinterposer material completely surrounds the holes, and has no internalstructure aside from the holes themselves.

Other designs for the interposer are possible as well, including designsthat incorporate some hollow space within the interposer itself. Inthese designs, the holes for the pins may resemble those in themonolithic design, but the interposer that surrounds these holes mayhave some structured hollow space in the regions surrounding the pinholes.

A specific example for such a structured interposer is shown in FIGS.30-33. FIG. 30 is a plan drawing of an interposer membrane, insertedinto a frame. FIG. 31 is a plan drawing of the interposer membrane ofFIG. 30, removed from the frame. FIG. 32 is a four-view schematicdrawing of the interposer membrane of FIGS. 30-31, with FIGS. 32 a-dincluding top-view, plan view, front view and right-side view drawings,respectively. FIG. 33 is a four-view schematic drawing of theinterposer, from the interposer membrane of FIGS. 30-32, with FIGS. 33a-d including top-view, plan view, front view and right-side viewdrawings, respectively.

In this specific example, the interposer 50 is structured as ahoneycomb, with supporting members 230 that extend between thepin-supporting holes 210, and generally empty space 240 between thesupporting members 230.

There are many possible designs for the supporting members 230 withinthe interposer. FIG. 34 includes 24 specific designs for the interposersupporting members, shown in cross-section. The holes 210 and thesupporting members 230 may take on any of a number of shapes, sizes andorientations. In these examples, the supporting members 230 may extendfrom one pin-supporting hole to a directly-adjacent hole, or from onepin-supporting hole to a diagonally-adjacent hole. Other orientations,shapes and sizes are possible, as well.

In general, the specific design for the interposer is chosen to haveparticular mechanical characteristics, rather than specific aesthetictraits. It is desirable that the interposer be vertically resilient, andprovide support and suitable resistance for the pins.

As seen in FIG. 34 showing 24 alternative structures, in addition tointerposer structure that is generally cylindrical (i.e., eachcross-section of the structure is the same, for all planes within theinterposer that are parallel to the contact plates), there may also beout-of-the-plane structure. For instance, FIG. 35 is a plan drawing ofan interposer having supporting/bridging members 260 that extend betweenadjacent holes within a particular plane, which may or may not be in thesame plane as the top or bottom edges of the cylindrical structures. Asanother example, FIG. 36 is a plan drawing of an interposer having asupporting plane 270 that completely fills the area between adjacentholes, but is absent above or below that plane. FIG. 37 includes 18specific designs for the interposer, shown in cross-section, where thetop and bottom contact plates are horizontally oriented, and the pindirection is generally vertical. As seen from the drawing, many possiblecross-sectional designs are possible.

In general, the interposer 50 need not be monolithic, and can includeone or more hollow regions with a design that can vary within the planeof the interposer membrane (as in FIG. 34) and can vary out of the planeof the interposer membrane (as in FIG. 35). Mechanical performance ofany interposer design may be simulated readily using finite elementanalysis.

In applications where there is a need to reduce contact resistance to aminimum, an effective solution lies is increasing the point contactpressure between the contact pin and the array contact. Of course, thiscould be done by increasing the insertion force but it has its limits.In addition, increasing the ablating/scraping action can remove oxidebuild up. Combining solutions provides the optimum result.

To increase the point contact pressure/force, without increasing theinsertion/actuator force overall, it is possible to reduce the contactsurface area with the embodiment shown in FIG. 38 which has a blade likeconstructions. The point contact pressure is actually increased (due tothe decrease in contact surface area. This has the additional benefit ofdecreasing the contact resistance, because the sharp blade constructionproduces a penetrating effect which reduces resistance by ablating oxideand by penetrating slighting into the ball contact to a place were oxidehas not yet formed. In FIG. 38, top pin 320 has a similar basic shape aspin 20 in previous embodiments except that the top surface 321 has beenaltered to provide the benefits mentioned above. The top pin has a topengagement surface 321 which engages electrical connections to a deviceunder test (20), the top engagement surface may include sharplongitudinal contact ridge 326 rising above the engagement surface 322,to an apex, the ridge extending at least along the major portion of theengagement surface. The ridge can be straight, planar, or curved and ornon linear. Sharp is desirable.

Unlike the fully planar surface 21 of pin 20, pin 320 has a split topsurface, with a first portion 322 being a planar strip extendinglongitudinally from one end to the other, and then a projection portion324 which rises from the surface 322 to a sharp or knife edge peak 326,creating a step to a planar wall 328. As visible in FIG. 41, on the backside of the wall 328, is a sloped wall 330 which terminates at an obtuseangle intersection 322 and rejoins the rear wall of the pin 320. Wall328 is position generally at a mid point along the lateral dimension ofsurface 322 so that the knife edge 326 is likely to strike the ball 2likewise near its midpoint where contact pressure will be greatest. Theback slope surface 320 need not be flat as shown but may follow anyshape so long as it can support the knife edge. Wall 328 likewise doesnot have to be planar, and may be sloped.

This above embodiment is only exemplary, as other designs are possibleso long as that increase point contact pressure, without increasingoverall pressure, and reduce resistance.

These goals are accomplished by making edge 326 sharp enough topenetrate (even microscopically), the surface on the contact 2. Thefirst few atoms on the surface of the ball are often oxidized but evenslight penetration can bypass that resistive layer.

For example, knife edge 326 may be skewed instead of parallel to thelongitudinal dimension. As seen in FIG. 39 in dotted lines or in acomplete view of its own in FIG. 42, it could follow a skewed path shownas line 326 a from points 400 to 402. By electing a now parallel pathbetween longitudinal ends of the pin top surface, there will beincreased ablation of the exterior surface of ball 2. This can befurther increased by making line 326 a follow a curved or serpentinepath (non-linear). This will further increase the ablation of the ballsurface. Likewise, a plurality of spaced apart notches/serrations in andalong the major part of the length of the knife edge would createadditional ablation and thus lower electrical resistance by scrape awayoxides.

The additional forms shown in FIGS. 12-19 also provide advantagessimilar to the embodiment in FIG. 38 and could be further enhanced iftheir surface was hemispherical or domed shaped (similar to thecurvature of FIG. 13 but having the features of FIGS. 12, 15-19. Somespecific examples of alternate configurations are shown in FIGS. 43-48

FIGS. 43 and 44 illustrate double sided domed knife edge peaks withcurved or hemispherical sidewalls 434 in FIG. 43 and steeper sidewalls436 in FIG. 44. The steep curved sidewalls of FIG. 44 provide for asharper knife edge which may be desirable in certain configurations.FIG. 45 shows a protecting land structure 426 having a generally planartop surface, generally planar parallel side wall 424 and generallyplanar shelf or ledge portions 422 a and 422 b on either side of theland 426. The location of land 426 shown at the midpoint across the topsurface of the pin is not required. It can be offset left or right orthe entire land can be skewed as in FIG. 42, but unlike FIG. 42, the topedge 428 is planar and not knife edged.

FIGS. 46 and 47 are variations of FIG. 45 where land 426 terminates in apeaked structure 430 with converging sidewalls. In FIG. 46, thesidewalls are first generally parallel from their base 422 a and thentransform into a triangular peaked shape with converging planarsidewalls. In FIG. 47 the parallel sidewalls are replaced withconverging sidewalls which taper from their base 422 c , which as shownmay be hemispherical, rounded or curved to a plateau where the taperedconverging sidewalls 432 rise to a peak

FIGS. 48-51 illustrates an embodiment which may be used in combinationwith all of the previous embodiments but is shown only in a knife edgeconfiguration for simplicity. Here a plurality of lands 440 (with recess440 a in FIG. 49 for example), 442, and 444 extend upwardly from thebase of the top pin are oriented into two or three parallel knife edgelands. They are shown as knife edged but can be any other top edge.Furthermore, they are shown as parallel but may be skewed as in FIG. 42,and the skew angle of each of the lands may be different so that thelines of the top edges form may intersect (in actual fact or at animaginary point distant from the pin).

The knife edge ridge 326 should be hardened if possible, such as byplating with hard gold under a beryllium copper which provides strengthand low resistance.

The spacing between lands 440 and 442 in FIG. 49 can be such that aball—style contact can reside partway received with in the recess 440 a.In the preferred embodiment, one-third to one half of the contact wouldbe received in the recess thereby providing for substantial contactsurface area and still create the scraping action which removes oxides.

The disclosure also includes a method of lowering contact resistancewithout increasing insertion force by creating a sharp edge of contactwhich can engage the IC circuit contact with a small surface area andconsequently high point pressure according to the disclosure herein. Itis also possible to also increase the drag (resistance) by slideablyengaging the pin and terminal then they are brought together and skewingthe longitudinal ridge on the top in. Various embodiments are shownwhich increase drag, thereby removing oxide build up. The pin surface isslideably engaged with the contacts on the IC by even the slightestlateral movement which occurs when the IC is seated during insertion.This lateral movement can be taken advantage of in addition to the abovementioned methodology of increasing contact force by reducing contactarea and increasing contact depth by penetration of the contact.

There is one notable further feature of FIGS. 30 and 31. The frame inFIGS. 30 and 31 includes a series of preferably peripheral mountingposts 220 that extend through corresponding locating holes 215 in theinterposer membrane. In FIGS. 30 and 31, the locating holes and postsare located around the perimeter of the membrane, although any suitablepost and hole locations may be used. In general, these posts 220 arearranged with great lateral precision, so that when a membrane is placedonto the frame, the pins in the membrane are also placed with greatlateral precision.

FIGS. 52-56 illustrate further alternative embodiments for the lower pin30 and follow similar numbering except increased by 500. In bothembodiments in FIGS. 52-56, the upper profiles are the same with face533B being flat (though the curvature of 23B is an alternative) and theback side 532 is curveted, (though a straight back side 32 is alsopossible.

The bottom portion/contact pad or foot 531A and 531B is howeverdifferent from the flat 31 foot in FIG. 5. In order to provide morereliable contact with the contact pad of the load board 4, the of bottomsurface 531A/B has a “foot” feature, being formed with a curve orarcuate shape, including a ridge which may also be arcuate or peaked invarious forms. In the case of 531A, it is an arc. In the pad of 531B,the preferred construction is that the foot includes a partial cylinder600 which has an arcuate bottom which extends over the middle portion ofthe entire foot 531B to create a “rocking” contact. The partial cylindercould also be a partial sphere, button, cube, ridge, pyramid or ball tocreate a rocking action in two axes, but the cylinder is preferred sothat the pin rocks on only one axis and stays aligned with the upperpin. The cylindrical portion can extend across the entire bottom widthor only a portion thereof and may contact a plurality of cylindricalslices spaced apart from each other to increase the oxide removingproperties of the foot. They may be a single arcuate/cylindrical shapeor a plurality of side by side parallel cylinders/arcs. In most cases,the edges and even the curvature will tend to scrape the oxide whenrocking action occurs as the DUT is inserted above. By the addition ofsuch feature, contact with the load board terminal will be focused overa small surface area and may further cause ablation of oxides on theterm by rocking action when the device under test inserted andlongitudinal displacement of the pins takes place. The ridge may alsoprovide a rocking action in response to impact of the DUT when itcompresses the interposer. The ridge may sharp or pointed such as shownin FIGS. 13-18 (except that they would be lower pins).

The result is also a method of lowering the resistance between aterminal on an integrated circuit and the load board achieved by makingthe bottom surface of the bottom pin non-planar, preferably arcuate.

The description of the disclosure and its applications as set forthherein is illustrative and is not intended to limit the scope of thedisclosure. Variations and modifications of the embodiments disclosedherein are possible, and practical alternatives to and equivalents ofthe various elements of the embodiments would be understood to those ofordinary skill in the art upon study of this patent document. These andother variations and modifications of the embodiments disclosed hereinmay be made without departing from the scope and spirit of thedisclosure.

1. In a contactor to be interposed between a contact load board and adevice under test, the contactor including a plurality of having aplurality of contact pads (4), each contact pad (4) being laterallyarranged to correspond to exactly one terminal (2), comprising: alongitudinally compressible membrane (10) for forming a plurality oftemporary mechanical and electrical connections between a device undertest (1) a longitudinally resilient, electrically insulating interposer(50) between the load board and device under test; a plurality oflongitudinally slideable, electrically conductive pin pairs (20, 30)extending through longitudinal holes in the interposer each pin pair inthe plurality being laterally arranged to correspond to one terminal (2)on the device under test (1); the plurality of pin pairs including a topand bottom contact, the top contact having a top engagement surfacewhich engages electrical connections to a device under test, said topengagement; the bottom contact for engaging a contact on the load board;the improvement comprising; said bottom contact which engages said loadboard includes a bottom surface, said bottom surface being arcuate. 2.The contactor of claim 1 wherein said bottom surface includes acylindrical ridge.
 3. The contactor of claim 1 wherein said bottomsurface includes a ridge extending downwardly toward said load board. 4.The contactor of claim 1 wherein said bottom surface includes a rockingmember for contracting the load board.
 5. The contactor of claim 1wherein said bottom surface includes a partial cylinder with its curvedportion for contacting a load board.
 6. The contactor of claim 1 whereinsaid bottom surface includes a sharp ridge.
 7. The contactor of claim 1wherein said bottom surface includes a plurality of sharp ridges.
 8. Thecontactor of claim 1 wherein said bottom surface includes a plurality ofparallel arcuate shapes.
 9. The contactor of claim 1 wherein said bottomsurface is non-planar.
 10. A method of lowering the resistance between aterminal on an integrated circuit and the load board having anelectrically conductive pin having a bottom surface engagable with theload board, the method comprising; forming the bottom surface to includean arcuate ridge along the surface, whereby engagement of the ridge withthe terminal will focus contact pressure over a small surface area andmay further cause ablation of oxides on the terminal.
 11. The method ofclaim 10 wherein the step of forming the bottom surface includes forminga cylindrical foot thereon.
 12. The method of claim 10 wherein the stepof forming the bottom surface includes forming a foot with a peakedridge thereon.